Does Horses' Waste Help or Hinder the Environment?

The average horse produces nearly nine tons of manure a year—that's a lot of poop! But did you know that all this manure could be both hindering and helping the environment?

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The average horse produces nearly nine tons of manure a year—that's a lot of poop! But did you know that all this manure could be both hindering and helping the environment?

Global warming is partly the effect of livestock production: grass-fed animals produce a digestive gas known as enteric methane, which contributes to the greenhouse effect, said William Martin-Rosset, PhD, head of equine nutrition research at the French National Institute for Agricultural Research (INRA) in Saint-Genès-Champanelle. But it's not all bad news: The compounds and minerals in equine manure can provide an excellent source of organic fertilizer as well as renewable energy, establishing the horse as a worthwhile contributor to sustainable development and a healthy planet, he said at the 2013 French Equine Research Day, held Feb. 28 in Paris.

Martin-Rosset and colleagues investigated equine enteric methane release, as well as horses' production of nitrogen, calcium, potassium, and other potentially harmful minerals through urine and feces. The researchers also looked into environmentally-friendly uses of equine manure.

Cattle produce about 90% of the enteric methane in France (which contributes to 3-5% of France’s global warming) while horses produce only 1.5% of the nation's methane, Martin-Rosset said. An average horse produces 20.7 kilograms (45.5 pounds) of methane gas per year—just a fraction of what cows produce annually. A lactating draft horse mare, for instance, will only release 34% of the methane released by a lactating dairy cow, he said.

The team also estimated that in a single year, the average horse excretes approximately 15 kilograms (33 pounds) of calcium, 10.5 kilograms (23.1 pounds) of phosphorus, 3 kilograms (6.5 pounds) of magnesium, 1.5 kilograms (3.3 pounds) of sodium, and 16 kilograms (35.2 pounds) of potassium (with 88% of that potassium in the urine alone).

“Our work reveals that equids are only weak contributors to global warming due to their anatomy and digestive physiology,” Martin-Rosset said.

Changing gears, Martin-Rosset described his team's work evaluating uses for horse manure. In France manure production—feces, urine, and straw—averages 12 metric tons per horse per year (based on a typical 500-kilogram [1,100-pound] horse), he said. That amount can vary according to the size of horse, feed consumption, kind of bedding, and how often the stall is cleaned. It’s better to compost the manure for at least two and a half months before using it as a fertilizer, he said. This allows a more efficient use of the rich nitrogen found in the manure, and it prevents soil contamination by unwanted seeds and pathogens.

Martin-Rosset also said that horse manure can also be an excellent energy source for renewable, environmentally friendly energy through methanization, a biological process that produces 60% methane and 40% carbon dioxide while creating heat or electricity. Methanization also produces a residue that is rich in nitrogen, phosphorus, and potassium, with very little waste. However, methanization can only really work with straw manure, as other kinds of bedding (i.e., wood shavings) would not produce as efficient results, he added.

Despite these benefits, Martin-Rosset cautioned that research is needed to explore the polluting effects of equine medications, remnants of which are also excreted into the manure. The University of Limoges in France is currently investigating these effects in detail, he noted.

About the Author

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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